Magnetostriction hydrophone



Patented Oct. 11, 1949 umrao STATES PATENT OFFICE 2,484,036 MAGNETOSTRICTION HYDROPHONE John R. Kauke, Washington, D. 0. Application April 16, 1945, Serial No. 588,515

' 3 Claims. (Cl. 171-385) (Granted under the a 1 amended April 30,

The present invention relates in general to microphones and more particularly to magnetostr-lction hydrophones.

An object of the invention is the provision of a device of the above type which shall be substantially non-directional.

Another object is the provision of a hydrophone capable of panoramic reception in at least one plane, and of small diametric dimensions in a plane of panoramic reception.

Another object is the provision of a device of the class described which shall be extremely comct of March 3, 1883, as

pact and sturdy, and capable of rough usage without substantial variation in sensitivity.

A further object is to provide a magnetostriction hydrophone which shall be simple in construction and easy to repair, and which shall be capable of being constructed from relatively inexpensive materials with a minimum number of parts.

Various other objects and advantages of the invention will become apparent from a perusal of the following specification and the drawings accompanying the same.

In the drawings:

Fig. 1 is a side elevation partly in section showing a hydrophone embodying the invention.

Fig. 2 is a side elevation looking from the right at Fig. 1, with the casing'in axial section and the inner elements in full.

Fig. 3 is a section on the line H of Fig. 1.

Referring to the drawings more in detail, the device comprises a pick-up coil iii wound upon a laminated iron core II and positioned within the middle portion of a tubular casing l2 of magnetostrictive material preferably nickel. Also within the tubular casing I! on each side of the pick-up coil and near the ends of the tube, are disposed permanent magnets 13 and i4 spaced from the pickp coil by spaced elements l5 and it of non-magnetic. non-conducting material such as Bakelite, wood or the like. To maintain the walls of the cylinder (2 substantially freely responsive to compressional waves, the spacer elements If: and it are given a cross-sectional contour, such that their area of contact with the cylinder will be a minimum. In the present instance they are of rectangular cross-section as shown and of such dimension as to lie loosely within the cylinder and not contact the latter at all fourcorners. Top and bottom end closures l1 and i8, preferably of nonmagnetic metal, in the present embodiment brass, seal the top and bottom ends of the tube, being secured to the tube by sweating with solder to the ends thereof at the adjoiningsurfaces l9 and 20 and further sealed by a fillet of solder as indicated at 2i and 22. A top spacer element 23 is positioned between the top end closure i1 and the top magnet to space the top magnet away from the top closure element so as to perm-it passage of a pair of circuit leads 24 over the top of the magnet and out through the tubular coupling 25 by way of a channel 26 in the spacer element. The circuit sions of the terminals of the pick-up coil l0 which latter, in the present embodiment is comprised of about 600 turns of number 36 DSE copper wire. wound about the laminated core ii and impregnated with insulating material in known manner. Magnets i3 and i4 may be of any suitable magnetizable metal capable of constituting a good permanent magnet. Alcino is to be preferred, and is what is used inthe present embodiment, since it produces a permanent magnet having a very high field flux density.

As shown in Figs. 1 and 2, the magnets l3 and I4 are mounted within the tube with their polar axes aligned parallel to the core of the pick-up coil with like poles facing in the same direction and, like. the coil core, extending diametrically across the interior of the tubular casing l2 preferably into contact with the walls of the casing or into very close proximity thereto so that the magnets, the core ii and a portion of the nickel tubular casing I! will be included in a common magnetic circuit.

Since the permeability of the laminated iron core I l and the nickel tube are both much greater than that of air, a large portion of the flux produced by the permanent magnets will pass from their north poles to their respective south poles by way of the laminated iron of the wall of the nickel tube. It will be understood, of course, construction to the pick-up coil stituted for the permanent magnets for production of the desired magnetizing field. Because the present embodiment is intended to respond to a band of compressional waves including superaudio frequencies the tubular casing i2 is formed with relatively thin walls, approximately 0.015 or one sixty-fourth of an inch, and a diameter of approximately one and seven-sixteenths of an inch, thus giving it a high, natural mechanical frequency in the neighborhood of the super-audio frequencies' ther physical characteristics of the particular embodiment here shown are that the tubular casing i2 has a length of approximately 7 inches, the pick-up coil core ii a crossleads 24 constitute extencore and a portionthat electro magnets similar in i0 may be subsection of approximately a half inch square. and the permanent magnets a height of about one and one half inches and a width of about one half inch. This leaves a spacing between the magnets and the core I I of about one and one half inches.

The above proportions and arrangement of parts has been found to produce in the walls of the nickel tubular casing l2 a high intensity of magnetization of a magnitude very favorable to effective utilization of the magnetostrictive properties of the tube. However, it is to be understood that considerable variation in the above proportions and arrangement of parts may be made without detriment to the operation of the device, the above specific embodiment having been described herein for the sake of disclosure and not for the purpose of limitation of the invention.

In operation, when the device is subjected to compressional waves as when submerged below the surface of a body of water through which compressional waves are passing, the body material of the tubular casing 62 will be subjected all round to variations in pressure, resulting in variations in the amount of flux passing through the magnetic circuit of the pick-up coil, and the production of voltage variations across the leads 24 corresponding to such waves, which voltage variations may be amplified in known manner for operation of suitable responsive means.

It will .be clear from the foregoing that the device is capable of panoramic reception in the sense of an equal response to sounds from all directions in a horizontal plane, particularly where the diameter of the tube is small in proportion to the wave length, for example less than a quarter wave length. The device has been found to lend itself well to use as a hydrophone for the reception of underwater sound in the neighborhood of super-audio frequencies. It has also been found to operate as a microphone in air, for which use the cylinder 2 should be made considerably thinner than one sixty-fourth of an inch.

While one specific embodiment of the invention -has been shown and described herein for the sake of disclosure, it is to be understood that the invention is not limited to such specific embodiment but contemplates all such modifications and variantsthereof as fall fairly within the scope of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is: a

1. A hydrophone comprising a water-tight tube of magnetostrictive material closed at each end, a pick-up coil disposed in said tube with its axis transverse to the axis of the tube, a permanent magnet disposed on either side of the pick-up coil within the tube with like poles pointed in the the axis of the tube, said pick-up coil and the permanent magnets being spaced apart along the axis of the tube, and a core comprising a laminated iron structure upon which said pick-up coil is Wound with its axis parallel to the polar axis of the magnets, whereby when the casing of said hydrophone is subjected to compressional stresses representative of under-water sound the permeability of said tube will be altered to vary the flux which passes through it and the pick-up coil with resultant voltage variations in said coil.

2. A hydrophone transducer comprising a closed hollow shell of circular cross-section in at least one plane and composed, in at least said circular portion, of magnetostrictive material, a pick-up coil and core therefor situated within said shell, said core having its axis positioned normal to the axis of said circular portion, and a magnet situated within the shell spaced to one side of said core and coil outside the coil with its polar axis suibstantially parallel to the axis of said core to establish a flux field independently of the coil including a substantial portion of said circular portion and the said core.

3. A hydrophone comprising a closed hollow cylindrical shell having at least its cylindrical wall composed of magnetostrictive material, a pick-up coil and core therefor situated within said shell, said core having its axis positioned normal to the axis of said cylindrical Wall, a magnet situated within the shell with its polar axis substantially parallel to the axis JOHN R. KAUKE.

' REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,966,446 Hayes July 17, 1934 1,985,251 Hayes Dec. 25, 1934 2,063,944 Pierce Dec. 15, 1936 2,063,950 Steinberger Dec. 15, 1936 2,153,571 Kallmeyer Apr. 11, 1939 2,207,064 Maurer July 9, 1940 2,249,835 Lakatos July 22, 1941 2,380,931 Batchelder Aug. 7, 1945 2,411,911 Turner Dec. 3, 1946 FOREIGN PATENTS Number Country Date 832,891 France Oct. 4, 1938' 

